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Abstract

The photon scanning-tunneling microscope (PSTM) yields optical
topographical images of samples that are thin or that are transparent
at the wavelength used. A range of sample sizes can be imaged
extending to well below the diffraction limit for sufficiently flat
samples. But samples of the order of several to many micrometers in
size can be analyzed with less-refined resolution if total internal
reflection can be made to occur in the sample. We used the PSTM to
examine the optical topography of mouse and human cells and of
chromosomes that are unstained. Our objectives were to demonstrate
the images as an alternative to conventional microscopy and to provide
a sample-preparation methodology that will later permit localized,
simultaneous fluorescence or absorption spectroscopy with the signals
collected by the probe tip. Furthermore, the PSTM’s ability to
produce optical profiles in air and in water was tested to establish
the basis for future investigation of possible abnormalities in the
chromosomes. That is, we considered both physical and biological
objectives. To this end we utilized the 442-nm line of a He–Cd
laser as well as the 633-nm line from a He–Ne laser, the resulting
image quality being tested partly to ascertain the increased effects of
scattering at the smaller wavelength. It is shown that adequate
resolution and signal-to-noise ratio can be obtained with the shorter
wavelength even in the presence of intensity fluctuations from the
laser, thus showing that fluorescence and absorption studies can be
expected to be practicable.

References

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